Might technically just be one? Peach’s Castle. They refer to the other one as Bowser’s Fortress. Frankenstein’s is more like an old manor with a tower, but I guess you can call it a castle. HTTYD has a cliffface and Fantastic Beasts has Parisian streets.
Magic Kingdom has three castles now, (if you count Beast’s Castle).
I believe the actual icon for the park will be the astronomical sphere over the entrance portal. The hotel in the back will function as a weenie for the hub.